85 years counteracting an invasion: chestnut ecosystems and landscapes survival against ink disease

A retrospective examination of early pest and disease outbreaks, such as ink disease, offers new insights into their impact on ecosystems and landscapes. Ink disease, caused by Phytophthora spp., is one of the most destructive diseases affecting Castanea sativa Mill. It first appeared in Europe in the early 18th century, with the initial recorded case in Italy (Piedmont) dating back to 1845. However, its spread instilled significant concerns in several chestnut-growing regions primarily devoted to fruit production. In 1938, a comprehensive assessment of Phytophthora xcambivora outbreaks was conducted in the Bolognese Apennines (Italy), providing a detailed overview of chestnut cultivation status. Thirty-six disease foci were documented, and laboratory tests confirmed the presence of ink disease. To understand the disease's impact on chestnut ecosystem and landscape over the past 85 years, the 1938 sites were revisited to assess chestnut persistence and phytosanitary status, with Phytophthora species detected using isolation and molecular techniques. Monitoring data revealed that C. sativa still thrives in all but one site, with its wood seemingly able to coexist in dynamic equilibrium with the disease. While P. xcambivora was still detected in several foci, the extent of damage appeared limited. The potential for natural control, likely influenced by the complexity of soil biota, along with the natural spread of hypovirulence in chestnut blight and biological control of the Asian chestnut gall wasp, could explain the continued presence of chestnut in the investigated area and potentially throughout the Italian chestnut range, despite nearly two centuries of ink disease prevalence. Nevertheless, ongoing monitoring is essential to dynamically comprehend the factors at play and their efficacy, particularly in the context of climate change and the possible spread of other Phytophthora species. The survival of chestnut ecosystems amidst ink disease underscores the preservation of the economic, ecological, and landscape values associated with these woodlands.